Hybrid device of hexagonal boron nitride nanoflakes with defect centres and a nano-fibre Bragg cavity

Solid-state quantum emitters coupled with a single mode fibre are of interest for photonic and quantum applications. In this context, nanofibre Bragg cavities (NFBCs), which are microcavities fabricated in an optical nanofibre, are promising devices because they can efficiently couple photons emitted from the quantum emitters to the single mode fibre. Recently, we have realized a hybrid device of an NFBC and a single colloidal CdSe/ZnS quantum dot. However, colloidal quantum dots exhibit inherent photo-bleaching. Thus, it is desired to couple an NFBC with hexagonal boron nitride (hBN) as stable quantum emitters. In this work, we realize a hybrid system of an NFBC and ensemble defect centres in hBN nanoflakes. In this experiment, we fabricate NFBCs with a quality factor of 807 and a resonant wavelength at around 573 nm, which matches well with the fluorescent wavelength of the hBN, using helium-focused ion beam (FIB) system. We also develop a manipulation system to place hBN nanoflakes on a cavity region of the NFBCs and realize a hybrid device with an NFBC. By exciting the nanoflakes via an objective lens and collecting the fluorescence through the NFBC, we observe a sharp emission peak at the resonant wavelength of the NFBC.

Electrical Control of Quantum Emitters in a Van der Waals Heterostructure

Controlling and manipulating individual quantum systems in solids underpins the growing interest in development of scalable quantum technologies1, 2. Recently, hexagonal boron nitride (hBN) has garnered significant attention in quantum photonic applications due to its ability to host optically stable quantum emitters3-7. However, the large band gap of hBN and the lack of efficient doping inhibits electrical triggering and limits opportunities to study electrical control of emitters. Here, we show an approach to electrically modulate quantum emitters in an hBN–graphene van der Waals heterostructure. We show that quantum emitters in hBN can be reversibly activated and modulated by applying a bias across the device. Notably, a significant number of quantum emitters are intrinsically dark, and become optically active at non-zero voltages. To explain the results, we provide a heuristic electrostatic model of this unique behaviour. Finally, employing these devices we demonstrate a nearly-coherent source with linewidths of ~ 160 MHz. Our results enhance the potential of hBN for tunable solid state quantum emitters for the growing field of quantum information science.

Spontaneous emission mediated by graphene/hexagonal boron nitride/graphene sandwich structure

Controlling the spontaneous emission of atoms or molecules is an interesting research topic in the field of quantum optics. Here we provide a perspective on modulating the interaction between two quantum emitters through a sandwich structure composed of graphene and hexagonal boron nitride (hBN). The dependence of interaction between quantum emitters on the thickness of hBN and chemical potential of graphene is investigated in detail. When the transition frequency of quantum emitter is located in the hyperbolic band of type I supported by hBN, the radiative state can be easily modulated by adjusting the chemical potential of graphene. So it is flexible to switch the interaction of quantum emitters from superradiant state to subradiant state by external electric field. When the transition frequency of quantum emitter is located in hyperbolic band of type II, the system can be always in the superradiant state. We predict the further research perspectives of spontaneous emission and superradiance with the help of metasurfaces based on two-dimensional materials.

DNA Self-Assembled Plasmonic Nanodiamonds for Biological Sensing

Nitrogen-vacancy (NV) centers in diamonds are promising solid-state quantum emitters for developing superior biological imaging modalities. They possess desired bio-compatibility, photostability and electronic spin-related photophysical properties that are optically accessible at room temperature. Yet, bare nanodiamond-based imaging modalities are limited by the brightness and temporal resolution due to the intrinsically long lifetime of NV centers. Moreover, it remains a technological challenge using top-down fabrication to create freestanding hybrid nanodiamond imaging probes with enhanced performance. In this study, we leverage the bottom-up DNA self-assembly to develop a hybrid plasmonic nanodiamond construct, which we coin as the plasmon-enhanced nanodiamond (PEN), for biological imaging. The PEN nano-assembly features a closed plasmonic nanocavity that completely encapsulates a single nanodiamond, thus enabling the largest possible plasmonic enhancement to accelerate the emission dynamics of NV centers. Creation of the PEN nano-assembly is size-independent, so is its broadband scattering spectrum that is optimally overlapped with the emission spectrum of NV centers. Study of the structure-property correlation reveals that the optimal condition for emission dynamics modification is causally linked to that for a plasmonic nanocavity. The cellular internalization and cytotoxicity studies further confirm the delivery efficiency and biological safety of PEN nano-assemblies. Collectively, the PEN nano-assembly provides a promising approach for manipulating photophysical properties of solid-state quantum emitters and could serve as a versatile platform to uncover non-trivial quantum effects in biological systems.

Optical properties of new hybrid nanoantenna in submicron cavity

An essential area of nanophotonics is the creation of efficient quantum emitters operating at high frequencies. In this regard, plasmon nanoantennas based on nanoparticles on metal (nanopatch antennas) are incredibly relevant. We have created and investigated a new hybrid nanoantenna with a cube on metal and quantum emitters. We demonstrate an increase up to 60 times for the rate of spontaneous emission and the gap-plasmon mode changing for nanopatch antenna in the metallic well. The results show the possibility of creating plasmon antennas in a controlled way by creating an array of regularly arranged nanoscale cavities-resonators.